--- a/dom/plugins/base/nsNPAPIPluginInstance.cpp
+++ b/dom/plugins/base/nsNPAPIPluginInstance.cpp
@@ -553,26 +553,31 @@ nsresult nsNPAPIPluginInstance::SetWindo
 
     PLUGIN_LOG(PLUGIN_LOG_NORMAL, ("nsNPAPIPluginInstance::SetWindow (about to call it) this=%p\n",this));
 
     bool oldVal = mInPluginInitCall;
     mInPluginInitCall = true;
 
     NPPAutoPusher nppPusher(&mNPP);
 
-    DebugOnly<NPError> error;
+    NPError error;
     NS_TRY_SAFE_CALL_RETURN(error, (*pluginFunctions->setwindow)(&mNPP, (NPWindow*)window), this,
                             NS_PLUGIN_CALL_UNSAFE_TO_REENTER_GECKO);
+    // 'error' is only used if this is a logging-enabled build.
+    // That is somewhat complex to check, so we just use "unused"
+    // to suppress any compiler warnings in build configurations
+    // where the logging is a no-op.
+    mozilla::unused << error;
 
     mInPluginInitCall = oldVal;
 
     NPP_PLUGIN_LOG(PLUGIN_LOG_NORMAL,
     ("NPP SetWindow called: this=%p, [x=%d,y=%d,w=%d,h=%d], clip[t=%d,b=%d,l=%d,r=%d], return=%d\n",
     this, window->x, window->y, window->width, window->height,
-    window->clipRect.top, window->clipRect.bottom, window->clipRect.left, window->clipRect.right, (NPError)error));
+    window->clipRect.top, window->clipRect.bottom, window->clipRect.left, window->clipRect.right, error));
   }
   return NS_OK;
 }
 
 nsresult
 nsNPAPIPluginInstance::NewStreamFromPlugin(const char* type, const char* target,
                                            nsIOutputStream* *result)
 {